1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, a process cartridge, and an electrophotographic apparatus.
2. Description of the Related Art
A surface of an electrophotographic photosensitive member is subjected to an external electric force or external mechanical force caused by charging, cleaning, or the like, and hence is required to have durability against such external force (such as wear resistance).
To meet the requirement, hitherto, there has been used an improving technology involving, for example, using a resin having high wear resistance (such as a curable resin) in a surface layer of the electrophotographic photosensitive member.
Meanwhile, problems resulting from an increase in wear resistance of the surface of the electrophotographic photosensitive member include image smearing and a reduction in cleaning performance.
A possible cause for the image smearing is a reduction in resistance of the surface of the electrophotographic photosensitive member. Possible causes for the reduction in resistance of the surface of the electrophotographic photosensitive member are: deterioration of a material used in the surface layer of the electrophotographic photosensitive member due to an oxidizing gas, such as ozone or a nitrogen oxide, generated by charging of the surface of the electrophotographic photosensitive member; and adsorption of moisture onto the surface of the electrophotographic photosensitive member. In particular, as the wear resistance of the surface of the electrophotographic photosensitive member increases, it becomes more difficult to refresh the surface of the electrophotographic photosensitive member (to remove the deteriorated material, the adsorbed moisture, or the like), and the image smearing becomes more liable to occur.
As a technology for suppressing the image smearing, Japanese Patent No. 5127991 describes that on the surface of the electrophotographic photosensitive member, depressed portions each having a depth of 0.5 μm or more and 5 μm or less and a longest diameter of an opening of 20 μm or more and 80 μm or less are formed so that the area of the depressed portions in a square region 500 μm on a side may be 10,000 μm2 or more and 90,000 μm2 or less, and a flat part contained in a portion other than the depressed portions is formed so that its area may be 80,000 μm2 or more and 240,000 μm2 or less. This can improve dot reproducibility even when the electrophotographic photosensitive member is left to stand under a high-temperature and high-humidity environment.
In addition, as a technology for improving the cleaning performance, Japanese Patent Application Laid-Open No. 2011-90296 describes a technology involving causing the surface of the electrophotographic photosensitive member to have an uneven shape having a plurality of depressed portions and a plurality of protruded portions, and controlling a surface roughness Rz of a top surface of the protruded portions so as to be 0.01 μm or more and 0.5 μm or less.
However, the technology described in Japanese Patent No. 5127991, though having a significant ameliorating effect on the image smearing, still has room for improvement in that when image output is performed under a low-humidity environment for a long period of time (on about 20,000 sheets), a streak-like image defect (hereinafter sometimes referred to as “low-humidity streak”) may be generated.
The inventors of the present invention have made an attempt to ameliorate the low-humidity streak by forming depressed portions each having a depth 0.5 μm or more and 5 μm or less and a longest diameter of an opening of 20 μm or more and 80 μm or less on the surface of the electrophotographic photosensitive member so that the area of the depressed portions in a square region 500 μm on a side may be 95,000 μm2 or more.
However, it has been found that there is room for improvement in that when an image having a low print percentage (about 1%) is output for a short period of time (on about 200 sheets) under a high-temperature and high-humidity environment, a streak-like image defect (hereinafter sometimes referred to as “high-temperature/humidity streak”) may be generated on a halftone image having a density of about 30% output thereafter.
Also in the case of using the technology described in Japanese Patent Application Laid-Open No. 2011-90296, no suppressive effect on the high-temperature/humidity streak has been able to be observed.